Resolution:
Product Restart is a reset of drive micro-controller. This is "equivalent" to a drive physical power OFF/ON. When Product restart is enabled, the drive reboots.
This function can be used, for example to reset a fault that can be reset only by drive power cycle. Instead to do a power cycle, you use the product restart assignment function, and the drive will reboot and clear the fault (of course if fault root cause has disappeared).

But keep in mind that RP and RPA are the same function:
Product Reboot.

RP: via parameter in keypad

RPA: via logical input.

Using Communications
Product Restart Assignment (RPA) is the same function but can only be commanded by logic input. It cannot be commanded via Communications
If you need to do a product restart via communication, the trick is to write to the RP parameter (Logic Address - 7128).
Via communication, you write the RP parameter equal to 1, and the drive will make a product restart.